If you’re unfamiliar, a combi boiler, short for combination boiler, is a compact and efficient heating system that provides both hot water for taps and central heating in one unit. Unlike traditional boilers, which require separate tanks for hot water storage, combi boilers heat water on demand, making them space-saving and energy-efficient options for modern homes. In contrast, alternative heating systems such as system boilers and heat-only boilers involve additional components like hot water cylinders or tanks, adding complexity and potentially reducing efficiency.

When considering how a gas combi boiler operates, it’s common to picture a straightforward process of water being drawn in, heated over a flame, and then delivered to taps as hot water. However, the reality is a bit more intricate:

  1. When you turn on a tap or switch on your heating, the boiler ignites a flame and cold water from the mains supply enters the combi boiler.
  2. The flame heats a heat exchanger. Water from the mains flows through the heat exchanger, absorbing heat from the flame.Contrary to popular belief, the water heated by the burner operates within an enclosed loop. This loop is pumped over the flame and through a heat exchanger. Now, imagine the heat exchanger as a loop where hot water flows in one direction and mains water flows in the opposite direction. The heat from the loop’s boiled water swiftly transfers to the mains water passing through in the opposite direction, rapidly heating it. The cooled water in the loop then returns over the flame for reheating, ensuring a continuous cycle.It’s crucial to understand that the hot water emerging from your taps doesn’t directly pass over the flame. Doing so would result in scalding temperatures. Instead, it absorbs its heat from the boiling water that has traversed the flame. This indirect transfer ensures that the water delivered to your taps is at a safe and comfortable temperature.Despite being called “boilers,” they don’t actually boil water in the conventional sense. Water boils at 100°C, transitioning from liquid to gas (steam). However, the water inside the boiler loop typically heats up to around 70°C, while the hot water that reaches your tap is around 55°C (or as per your desired setting). For context, a pleasant hot bath is around 40°C, while a baby’s bath should not exceed 37°C.
  3. The now-heated water is delivered directly to taps or showerheads whenever hot water is requested.Beyond tap water, when heating is required, hot water is circulated through radiators or underfloor heating systems to warm the living space, providing instant heat whenever you need it.

By visualising this intricate process, you gain a deeper understanding of how a gas combi boiler efficiently heats water, ensuring both comfort and safety throughout its operation.

If you are in need of a boiler installation, service or repair and located within our service area, don’t hesitate to contact the Maintracts team today, we’d love to help you.